Inflatable Elastomeric Plug For A Dual Containment Piping System

ABSTRACT

An inflatable annular plug for use in creating a seal between an outer conduit and an inner conduit in a dual containment piping system comprises an annular structure for fitting into the piping system. A first connector is bonded to the plug for enabling the plug to be inflated by an external fluid source. A second connector extends through the plug in an axial direction for enabling fluid to flow through the plug and is bonded to the plug at both entrance and exit points. An outer surface of the plug is formed with a plurality of circumferential ribs and lands to form a plurality of axially spaced seals between the outer conduit and the plug. The plug is used in conjunction with a second plug to form a sealed test space between plugs.

SPECIFIC DATA RELATED TO THE INVENTION

This application claims the benefit of U.S. Provisional Application No. 60/692,616, filed Jun. 22, 2005.

The present invention relates to dual containment pipe systems and, more particularly, to a method and apparatus for leak testing of annular spaces between inner and outer conduits in such systems.

BACKGROUND OF THE INVENTION

Dual containment pipe systems are utilized in applications in which leakage of a fluid would create undue danger or environmental damage. The systems include an inner pipe or conduit, sometimes referred to as a “carrier” pipe, for carrying a fluid and an outer pipe or conduit, sometimes referred to as a “containment” pipe, through which the inner pipe extends. By way of example, such systems may be used in chemical plants, landfill applications, in sewer systems or in petroleum product conduit systems. The dual containment system isolates and dual contains the effluent or the chemical product from its original environment in the host or inner pipe so that any leakage from the inner pipe is further contained within the space between the inner and outer pipes. Dual containment systems are well known in the art and the methods and apparatus for maintaining spacing between the inner and outer conduit are also well known.

The intent of the outer pipe or conduit in a dual containment system is for containment in the event of a leak or rupture in the inner conduit and not to provide an auxiliary path for fluid flow. Accordingly, it is important to maintain the integrity of the host or inner pipe to minimize the opportunity for leakage into the outer containment system. It is also important to maintain the integrity of the outer conduit or pipe so that in the event of leakage of the inner pipe, the fluid is maintained by the outer pipe and not allowed to leak into the environment. It is therefore important to provide some method and apparatus for checking the integrity of the inner and outer conduits of a dual containment system.

BRIEF SUMMARY OF THE INVENTION

In a preferred embodiment, the present invention is disclosed in the form of an inflatable and expandable annular apparatus that may be characterized as donut shaped or shaped similar to a tire inner tube having an inner opening of a diameter sufficient to allow the apparatus to be placed such that an inner conduit of a dual containment system slips into the inner opening of the apparatus. The apparatus is sized such that upon inflation, the apparatus expands to form an air-tight seal around the inner conduit and against the outer conduit. The apparatus may be formed of a fiber reinforced elastic material such as a nylon reinforced styrene butadiene rubber (SBR). The material of the apparatus may be of different thicknesses depending on the particular application, i.e., the type of containment system being tested and the environment or liquid being transported. For example, the material may have a thickness that ranges from about one-half inch to one and one-half inch.

The apparatus is used in pairs so as to isolate a section, i.e., a test space, of a dual containment system. A section may be short, such as measured in inches, if the testing is being conducted on a fitting, or a section may be measured in thousands of feet if the testing is being conducted on an extended length of pipe. In either case, each annular apparatus is inflated to an appropriate pressure such as, for example, between 35 and 80 pounds per square inch (PSI) to form a complete seal at each apparatus that isolates a section of the containment system to be tested. Other pressures may be used depending on the size of the conduit, the material of the conduit, the pressure requirements of the conduits and other characteristics of the inflatable apparatus. Thereafter, the annular test space defined by the apparatus and the inner and outer conduits is pressurized and monitored to detect any leakage. The test space may be pressurized with air or a selected gas or even a liquid depending on the particular conduit undergoing testing. The pressurizing fluid is preferably introduced through piping passing through at least one of the annular apparatus. The piping passes through holes formed in the apparatus with the holes being sealed to the piping by adhesively bonding or other chemical reaction depending on the type of material used for the apparatus and the piping. Two pass through pipes are presently used, one for pressurizing the test space and the other for monitoring the pressure in the test space. Any leakage in the inner or outer conduit will result in a pressure drop in the monitored pressure. It will be noted that an advantage of the present system is that the inflatable annular apparatus does not have to be precisely sized to fit the containment system since the apparatus can be expanded by inflation to create an air-tight fit. This is an advantage in that the size, i.e., the diameter, of the space between the inner and outer conduits vary between manufacturers and as a function of the required wall thickness of the conduits as well as the environment in which the dual containment system is being used. Such variations may be due to differences in wall thickness of the various conduits used in forming dual containment systems as well as tolerances in the manufacturing process.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawing in which;

FIG. 1 is a perspective view of an exemplary installation of the invention;

FIG. 2 is an end view of the installation of FIG. 1; and

FIG. 3 is a perspective view of three different size inflatable plugs of the present invention.

DETAILED DESCRIPTION OF ONE FORM OF THE INVENTION

Referring now to FIGS. 1 and 2, there is shown a perspective view of a pair of annular inflatable elastomeric plugs 10 and 12 and an end view of the plug 10 constructed according to one form of the present invention. The plugs 10, 12 are shown installed within a demonstration conduit 14 formed of a rigid transparent plastic material to enable viewing of the plugs. The conduit 14 represents a conventional outer containment conduit that, in commercial use, may be stainless steel or other suitable material that may be joined, fused or welded to create a continuous length of pipe. The inner conduit 16 is shown in an opaque material. FIG. 3 should be referred to for a perspective view of a plug 10 without the conduit and for illustrating that the plugs are constructed in different diameters and different lengths for different applications.

Turning again to FIGS. 1 and 2, each of the plugs 10 and 12 may be mirror images so that each is constructed with an inflation connector 18 and a pair of pass-through connectors 20 and 22. The connector 18 is connectable to a source of pressurized fluid such as air, gas or liquid to allow the plug to be inflated and expand to form a seal between the outer conduit 14 and the inner conduit 16. Note that the plugs 10, 12 expand both inwardly and outwardly to form the inner and outer sealing relationship with the inner and outer conduits 16, 14 respectively. Each of the connectors 20, 22 attach to pipes 24 a, 24 b that pass completely through a plug. The pipes 24 a, 24 b are bonded to the plug at at least both their entrance and exit points and preferably along the entire length of the plug, either by chemical bond or heat bond. If the pipes 24 are formed of metal such as, for example, stainless steel, steel, or aluminum, the bond may be an adhesive or chemical reaction bond or by heating the plug material to a liquid temperature at the joint to form the bond. Different types of bonding techniques that vary with the types of materials used for the plugs and pipes are well known in the art and could be considered for the present application. Similarly, the connector 18 attaches to a pipe 26 that passes through an end wall 28 of the plugs 10, 12 and is sealed to the end wall in a manner similar to the pipes 24. However, the pipe 26 terminates within the plug so that the plug can be inflated by fluid pumped into it through the pipe 26. One of the exiting pass-through pipes 22 can be seen in FIG. 1 at 22 a.

As can be seen from the figures, the structure of the plug 10 (plug 12 being identical and the plugs being used in pairs to isolate a section of dual wall containment piping) is generally axially longer that its diameter. However, the plug need only being as long as is necessary to retain the particular pressure in the test space and therefore may be shorter than the diameter in some applications. Further, the plug 10 is preferably formed with a plurality of annular ribs 28 separated by landings 30 so that the outer circumference has a generally corrugated appearance. The ribs and landings provide multiple, spaced contact areas and enhance the sealing relationship. When the plug 10 is inflated, these ribs press outward into contact with the outer conduit and form a plurality of spaced seals along the length of the plug.

While the three sizes of plugs illustrated in FIG. 3 provide some indication of the variation in plugs, the following table illustrates how a particular size plug would be selected for use in testing a dual containment system. The table is provided for illustrative purposes only and is not intended to represent the full range of dimensions with which the invention may be used by manufacture of the plugs in different sizes with different wall thicknesses for use with different pressures. Carrier Pipe Min Containment Pipe Max Containment Pipe Min/Max Product # O.D. I.D. I.D. Differential 2″/4″ DCTP 2.375″  3.633″ or 4″ SDR 11  3.938″ or 4″ SDR 17 1.25″ to 1.55″ 3″/6″ DCTP 3.5″  5.349″ or 6″ SDR 11  6.084″ or 6″ SDR 26 0.925″ to 1.292″ 4″/8″ DCTP 4.5″  6.963″ or 8″ SDR 11  7.921″ or 8″ SDR 26 1.232″ to 1.711″ 8″/10″ DCTP 6.625″  8.879″ or 10″ SDR 11  9.874″ or 10″ SDR 26 1.027″ to 1.625″ 8″/12″ DCTP 8.625″ 10.293″ or 12″ SDR 11 11.711″ or 12″ SDR 26 0.834″ to 1.543″

In using the present invention, it is necessary to have access to an open end of a dual containment system so that the apparatus, i.e., the plugs 10 and 12, can be inserted with the inner conduit passing through the hole in the center of the plugs. In general, it is necessary to have access to each end of the containment system on opposite sides of the area to be tested. Once the plugs 10, 12 are positioned in the containment system, the connectors 18 are coupled to a source of pressurized fluid, such as air, and the plugs inflated to create an air-tight space in the containment system between the two plugs. The plugs may be inflated to a pressure between about 35 and 80 PSI depending on the elasticity of the material of the plug, the reinforcement material used in the plug, the elongation of the plug, the diameter or span of the plug and the back pressure to be used in the test space. Such a space is indicated at 32 in FIG. 1. Thereafter, another fluid source is connected to one of the connectors 20, 22 and a pressure sensor (not shown) connected to the other of the connectors 20, 22. The pressure sensor may be a conventional pressure gauge of a type well known in the art that threads into one of the connectors 20, 22. The space 32 is then pressurized to a desired value and the source of pressurized fluid cut off at the desired value. The pressure in the test space 32 is then monitored to detect any drop that could be due to leakage in either the inner or the outer conduit of the containment system. While it is preferred to use two pipes for testing the space 32, it will be recognized that it may be possible to use a single pipe for both pressurizing the space and monitoring for pressure drop.

While the invention has been described in what is presently considered to be a preferred embodiment, various modifications and adaptations will become apparent to those skilled in the art. Particular attention should be paid to the range of sizes and pressures used in inflating the inventive plugs since such values will vary depending on the particular application and the type of material used for the application and the wall thickness of the plug required to support an application. It is intended therefore that the invention not be limited to the specific disclosed embodiment but be interpreted within the full spirit and scope of the appended claims. 

1. An isolation system for isolating a test space in a dual containment piping system having an inner conduit and an outer conduit in spaced apart relationship, the isolation system comprising: a pair of annular inflatable plugs, each of the plugs having at least one pipe passing axially therethrough and at least one pipe passing thereinto, each of the pair of plugs being sized to slide into the piping system with the inner conduit fitting into a central opening in the plugs and the plugs being spaced apart to define a test space therebetween; connector means coupled to the at least one pipe passing thereinto for enabling a flow of fluid into the plugs to inflate the plugs and form a seal at the interface of the plug with both the outer conduit and the inner conduit; connector means coupled to the at least one pipe passing axially through the plugs for enabling a flow of fluid into the test space between the plugs for establishing a predetermined pressure therein; and pressure sensing means for monitor the pressure in the test space to detect a pressure drop therein.
 2. The isolation system of claim 1 and including a second pipe passing axially through the plugs for enabling continuous sensing of pressure in the test space.
 3. The isolation system of claim 1 wherein the plugs comprise nylon reinforced SBR.
 4. The isolation system of claim 3 wherein the plugs having a wall thickness of between about 0.5 inch and 1.5 inch.
 5. The isolation system of claim 4 wherein the plugs have a corrugated outer circumference defined by a plurality of alternating annular lands and ribs.
 6. The isolation system of claim 5 wherein the test space is pressurized to a pressure of between about 10 and 15 PSI.
 7. The isolation system of claim 5 wherein the plugs are inflated to a pressure of between about 35 and 80 PSI.
 8. An inflatable annular plug for use in creating a seal between an outer conduit and an inner conduit in a dual containment piping system, the plug comprising: an annular structure having a length at least as large as a diameter of the plug in an inflated condition; a first connector bonded to the plug for enabling the plug to be inflated by an external fluid source; a second connector extending through the plug in an axial direction for enabling fluid to flow through the plug, the second connector being bonded to the plug at entrance and exit points thereof; and an outer surface of the plug being formed with a plurality of circumferential ribs and lands to form a plurality of axially spaced seals between the outer conduit and the plug.
 9. The inflatable annular plug of claim 8 and including a third connector extending through the plug in an axial direction for enabling monitoring of pressure on one end of the plug from an opposite end thereof.
 10. The inflatable annular plug of claim 8 wherein the plug is formed of a fiber reinforced expandable SBR material.
 11. The inflatable annular plug of claim 10 wherein the wall thickness of the plug is between about 0.5 and 1.5 inch. 